I have been trying to tune the Holley commander for almost a year and it seems to make no sense.

Is the narrow band oxygen sensor really of any use ? I cannot get the system to calm down.

If someone out there can suggest a document other than the Holley Manual, a step by step manual that tells you how to tune the Holley TBI commander for normal day to day driving, I would appreciate it. It runs oK now but gets 6-8 miles per gallon and I know this is not right.

Example: I finally found a fuel map that works well (TBI350) but I know it's way too rich the because of the way it sucks gas. The cells at idle were around 22 or 23, and I leaned the cells all to 15 and it worked well, but the O2 comp did not change at all, stuck at 82% (max rich). Then I leaned the cells to 14 and the engine started to run really crappy, hunting surging, etc. Not working well at all.

Anyway this has me stumped. The O2 sensor seems to be just randomly wandering up and down the scale from 82 to 102, no rhyme or reason, and no amount of leaning it out seems to calm it down.

I am thinking only a wideband O2 sensor will work but I don't want to spend another $300 to replace something that is supposed to work somewhat.

Any suggestions on how to make this narrow band O2 sensor do SOMETHING rational?

Narrow band is hard. It knows only "rich" "lean" and "Stoch" nothing else.

That said, going from "running good but showing -82%" to lean surge with a one number change seems weird.

Almost makes me wonder about the rest of your setup, engine specs, timing, etc.

One thing I can give you... a Commander 950 TBI CAN work. I'm running a 900 w/85lb injectors on a near 500 hp 383, just in the final stages of tuning. I have a wideband, as well as electronic timing control.

She's idling at 14.7, cruising at 15.5, and getting very near 20 mpg!

One "Standard check" that I hope you didn't skip is actually checking return line pressure with a gauge. Pressure in the return line will completely screw up this (or any other efi's) ability to idle.

My return line is a 5/16" rubber fuel line into a 3/8 steel fuel line straight into a return fitting on the fuel tank. No restrictions that I know of. I will however take my fuel pressure gage (yes I have one) and measure the return line. The return line is the same size as the fuel supply line. Is that too small a return line? 3/8 steel fuel line? The manual recommended 5/16 but I went a bit larger.

On the supply side, I measured the fuel pressure after I had it running and it was 14 psi, I believe. It seemed low at the time but I checked the manual and it was within spec.

The fuel return flows like a river, I can hear it running into the tank, so I see no reason for backpressure, but I will check tonite.

I have done a lot of tuninge tweaking and improving, and have been through a couple O2 sensors, and believe I have one now that works.

Let us know on the return pressure.
The return line should be the same size as the supply, so you should be ok there.

14 psi is low but not out of range. Spec is 21. I run 16 psi on mine, injectors are a lil big and the FP needed to be lower to lean the idle enough.

Fuel return line pressure is about 2 psi. As close to zero as my 100 psi gage will read. No surprise there. The fuel return is plumbed as it should be.

I have been tinkering with the fuel map cells at idle. The engine idles very smoothly if the fuel map cells are anywhere between 14 and 33. The O2 sensor stays at about 0.60 to 0.70 volts, which is yellow in the O2 voltage box, when the engine is idling comfortably in this 14-33 fuel map zone.

I have been able to drive the O2 voltage reading above about 0.75 (window changes to green) and below 0.30 (window changes to red) by changing the fuel cell value to values way out of the 14-33 range. Right at 13 the engine starts to hunt and the IAC begins to open, and generally it's not happy. Below 13 it wants to die. Then the O2 voltage starts swinging wildly.

So the O2 sensor is not telling me anything I can't already tell by just listening to the engine. If you go WAY outside the nominal fuel mixture, the engine won't run smoothly, and the O2 swings back and forth wildly, and inside the nominal zone, the O2 sensor just sits on about 0.64 volts, which according to chart is 14.7....

Given what I have read about the narrow band O2 sensor, I am not surprised, I just can't figure out how to do anything useful with the O2 readings.

Any more ideas ??


thanks for your Help,


Andy

The narrow band o2 is "in the green" only within a couple tenths of 14.7:1.

Many engine simply won't idle there, tho most will.

Work it as if it were carbed. If someone told me thier car idled stinky rich, and thier mixture screws had no effect, I'd tell them to crank in some timing.

Where's your timing?

I'm currently very conservative at 25 degrees at idle. She idles @ 800 rpm, about 14.4:1 afr, with 22 in the idle cells. (note the actual idle cell numbers depend a lot on injector size and fuel pressure, mine are 85's, @ 16 psi.)

What's your pulsewidth at idle? Below 1.8 is to fast for the injectors to open and close properly. That's why I lowered my fuel pressure, was below 1.8 and funky idle @ 21 psi, now is 2.8 and good idle @ 16.

you really need to get wideband, and I'd recommend one with a dash gauge. You can use anything with the c950 system, as long as they tell you it's voltage to AFR table. I use an autometer, many use LC1, nothing wrong with Holley's setup either.

You need v3 firmware in the ECU, and v3 s/w to use wideband.

The engine is stock and the timing is stock, 8 degrees at idle, and a whole bunch of advance with the vacuum and mechanical advance.

At idle the pulse width and duty cycle are both about 1.8 - 2.0.

Actually it runs fine, and idles smoothly, it just eats a lot of gas and I think it's way too rich.

I will look into a wideband O2 sensor and see about installing it.

Is your timing controlled by the c950?
Do you have a vacuum advance if it isn't?

You need more timing. A lot more.

If you don't have a computer controlled distributor, look on ebay. I bought mine for $57!
You can also get one out of a junkyard from near any late 80's V8.
You can do some cool stuff with computer controlled timing that simply isn't possible with conventional advance systems.

The distributor is a Unilite with vacuum and mechanical advance. At idle the advance is 8 deg BTDC. At 25000 rpm the vacuum and mechanical advance takes it up to 28-30 Deg BTDC.

I am planning to get a digital distributor, I just have not got there yet. I don't like to change too many things at once. THis machins started stock, then I put in the unilite distributor (much better) and then removed the 4 bbl carb and put on the EFI.

What should the advance be at idle, and at 3000 rpm, for best performance with the O2 sensor ?

I'd go with the computer controlled distributor right away. It's not changing something else, it's part of the system...

Timing at idle (initial plus vacuum conventially) needs to be 25 to 35 degrees.
Cruise vacuum will approach 50 degrees.
"total timing" checked with the vacuum advance discnnected must be no more than 38, possibly as low as 32-34 depending on head design.
"initial timing (vacuum disconnected) wants to be around 18.

It is getting awful hard for me to think in terms of initial and total anymore.
Getting used to that 16 by 16 grid and "anything goes" adjustments.

Well certainly, depending on cam, and compression of your engine, timing can be a very personal thing, but if I do go and mess with the timing, I think the limiting factor on timing advance must be knocking...(detonation?) if the engine is knocking, the the timing advance is a bit too far....is this true ? Knocking is definintely a no-no, as I recall.

I had an inspired thought yesterday, and opened up the fuel map. I then loaded my favorite Holley factory fuel map, 350TBI, did a cell select of all cells, and subtracted 5 units from all cells.

Then I started the car, warmed it up, drove it a bit, and found the O2 sensor was behaving exactly the way it was supposed to. I then did a few more global subtract operations from the fuel map. and found that at -12, it was too lean (finally) and at -9 it seemed to work best all around.

Now the O2 sensor is happily bouncing back and forth from 0 to .6 and back to 0. The datalogs look pretty good, and it runs smooth. Now if I can just get some reasonable gas mileage out of it.

Right now I have factory timing but will crank it up per your last reply and see what happens.

Well it really depends on the engine to see what timing you need 18 initial can be pretty high on a stock engine.

Yes thats what a narrow band should do bounce between .2 and under to about .8-1.2 volts depending on the sensor which means its stoich.

Just a side note recent article shows that detonation and knocking are two seperate things but detonation can be identified by knocking.